Stents are used to a continuously increasing extent in modern implantation technology for stabilizing/supporting hollow organs. The approach appears particularly suitable for coronary cardiac illnesses such as acute myocardial infarctions, which represent one of the most frequent causes of death in Western Europe and America. In more than 80% of the cases, the cause of the myocardial infarction is the thrombotic closure of a coronary artery through rupture of an atheromatous plaque upon pre-existing stenotic atheromatosis. Decisive factors for the long-term prognosis after acute myocardial infarction are (i) effective and long-standing reopening of the infrarcted artery, (ii) a duration of the thrombotic vessel closure, (iii) preventing greater myocardial loss and ventricular remodeling, and (iv) managing of rhythmogenic complications. The cited factors determine not only the cardiovascular mortality, but rather also the quality of life after the infarction.
For more than 20 years, nonoperative methods for stenosis treatment have been established, in which the constricted or closed blood vessel is expanded again, inter alia, by balloon dilation (PTA, percutaneous transluminal angioplasty). This procedure has proven itself in particular in the treatment of acute myocardial infarction. To prevent renewed closure of the expanded vessel by obstruction, a stent is used.
An application system is necessary for introducing and precisely placing the stent—referred to in the following in summary as application. The system comprises two components: the implant itself and a catheter, using which the application of the stent may be performed. Both components must be tailored to one another to perform the application of the stent as reliably as possible and with minimum operative effort.
On the part of the stent, a structure is to be provided which supports the implantation procedure and, in addition, ensures that the desired functionality may be observed at the implantation location. This is achieved, inter alia, in that the tubular stent is designed as expandable; upon application, the stent is first brought in a non-expanded state to the implantation location and transferred there using suitable means to an expanded state. The expansion may be caused by application of a mechanical force, e.g., inflation of a balloon, or may result from a structure itself, if memory materials are used in the stent, for example.
On the part of the catheter, adaptations are required, inter alia, as a function of the stent type used: one differs between self-expanding stents and balloon-expandable stents. For the first stent type, means must be provided which induce the self-expansion of the stent. The latter stent type makes the use of a balloon catheter necessary, and the stent is expanded at the implantation location by inflation of the balloon.
A partial problem in optimizing application systems for stents of this type is preventing slipping or even loss of the stent during the transport to the implantation location and during the implantation. One approach provides coating the stent supported on the catheter using a protective film which entirely or partially covers the stent. The film is typically to be composed so that the film either tears upon expansion of the stent or may be elastically stretched together with the stent. The approach will unavoidably result in parts or the entire film remaining in the body and a mechanical resistance of the film influencing the expansion behavior of the stent. Furthermore, a circumference of the application system is enlarged.